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Post by gatorflash1 on Dec 27, 2018 13:48:06 GMT -5

I have heard that some tumbler folks do this to get more of the red colors into their plain polished banded agates. Some say it is done naturally if the agates are taken from iron rich soils like those in Madagascar. Many times I have found a reddish crust on my rough agates. Any info on coloring polished agates would be appreciated.

Post by zarguy on Dec 27, 2018 14:06:01 GMT -5

gatorflash1 - I haven't tried anything like that.I buy the same Madagascar tumbled agates you show in your avatar.When cut open, they are white/gray inside.They're either heat treated or heat treated with additives.I wish I knew the process, because I'd cab it & then bring out the color afterwards that was ground away.Lynn

Post by gatorflash1 on Dec 27, 2018 16:44:33 GMT -5

The coloring seems to be just on the surface. From what I understand heat treatment usually effects the entire stone's appearance, not just the surface. Lots of agates and other stones are dyed after being cut and polished.

Post by pauls on Dec 28, 2018 15:14:00 GMT -5

I haven't done this but apparently the treatment to get brown is soak in sugar solution then in hot sulphuric acid, the acid carbonises the sugar. Sorry no link I saw it just the other day somewhere and of coarse now can't find it.

parfive
God of Multiple Parallel Universes Full of Rocks and Apprentice to THE ONE.

Consider the Earth’s history as the old measure of the English yard, the distance from the King’s nose to the tip of his outstretched hand. One stroke of a nail file on his middle finger erases human history.

Post by rmf on Dec 28, 2018 19:59:40 GMT -5

I have soaked agate in a copper nitrate solution and got a light blue. That worked well. I have also take brown chalcedony and roasted it in the oven and made carnelian. That worked well too. I tried to make black onyx and that failed miserably. Try soaking your agate in Ferrous Sulfate. You should be able to find that at an ag place as a soil conditioner. It turns brown like limonite (Fe2+) but then I suspect you will need to roast it in the oven to turn the Iron Ion to a Fe3+ red hematite Ion. Let us know how it goes.

Post by NRG on Dec 29, 2018 8:55:03 GMT -5

The coloring seems to be just on the surface. From what I understand heat treatment usually effects the entire stone's appearance, not just the surface. Lots of agates and other stones are dyed after being cut and polished.

Heat treatment only effects the area heated. So a torch on the surface for a few seconds will color the visible area but not deep inside.

Post by zarguy on Jan 5, 2019 12:40:19 GMT -5

The heat treatments I've heard about done by knappers, involve packing stones in sand and heating in an oven,slowly bringing the heat up to a set temp.Then leaving it at that temp for a set length of time.Then letting it cool down over a long period of time.Supposedly this heats the stone to the core.The sand distributes the heat evenly to the stone.The gradual ramp up & down keeps the stone from fracturing.Maybe heating for a shorter time (as with a torch) doesn't get the core up to the same temp.I've never done it.Someday maybe.Lynn

Post by agatemaggot on Jan 5, 2019 13:21:53 GMT -5

Heat treating Knapping material removes the moisture from the rock and usually makes it more brittle and easier to flake. Some stone is like a sponge and other is like holy crap hateful ! Has to be on the brittle side .2 hours at 200 deg.Start ramping up at 50 deg. per hour until 450 is reached for Montana550 to 750 for other type of stone.Turn off heat source and let stone cool while buried in the sand.Got the specifics from a Geologist from Oregon that Flintknaps can't remember his name.This process changes the color of the Iron and other minerals in the stone also .Some stone requires different heat from different areas of the deposit.

Careful with the torch business, raw stone has enough moisture in it that you ( WILL ) re-invent Popcorn .The old timers story about seeing an Indian drip cold water on a hot rock is TOTAL B.S.!You needn't ask me how I know THAT ! Sorry about hijacking your post !Harley

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